The present invention relates in general to a light combiner for image projection systems, and, more specifically, to a multi-prism system for directing colored light sources along a common output light path.
Various types of video projection systems are in common use today. An imaging device such as a Digital Light Processor (DLP) or Liquid Crystal on Silicon (LCOS) device are illuminated by and selectably modify light according to an instantaneous frame of a video image. To keep the size, weight, and cost of such projectors to such a minimum, the video projection system usually uses only a single imaging device while producing a color image. The device is sequentially illuminated with red, green, and blue portions of the image. This mode of operation is called field-sequential color. The illumination source or light engine for this type of color video projector includes separate red, green, and blue light sources that are turned on individually during the appropriate portion of a video frame. In order to use a single image forming device, the separate colors must illuminate the image device along the same light path leading to the device.
Light engines using red, green, and blue light emitting diodes (LEDs) on a single common substrate generally suffer from efficiency and/or color uniformity problems. For example, the individual LED dice may be difficult to locate in an optimum position relative to the collimating optics. Known light engines using separately-positioned sources for each color of light generally use a system of dichroic mirrors to combine the light outputs of the separate sources. Known mirror systems are large and expensive, and it has not been possible to efficiently integrate them in a compact, low-cost light engine.